A bottom and top coat for deep embossing resistant household appliance panels and a preparation method thereof

Abstract

The present invention discloses a bottom and top coat for deep-embossing-resistant home appliance panels and a preparation method thereof. The bottom and top coat comprises the following components in parts by weight: 20-35 parts of a modified polyester resin, 3-10 parts of a high-molecular-weight polyester resin, 6-10 parts of a curing agent, 20-35 parts of a pigment and filler, 0.4-1 parts of wax powder, 2-3 parts of an auxiliary agent, and 15-30 parts of a mixed solvent. The modified polyester resin is a polyester polyurethane resin, which is prepared by the addition polymerization reaction of a polyester polyol resin and a diisocyanate compound. The single coating formed by the bottom and top coat for home appliance panels prepared by the present invention has excellent adhesion, machinability, corrosion resistance, and adaptability to different types of substrates, and in particular has good deep-embossing resistance, and has broad application prospects in the color-coated board market.

Description

Technical Field

[0001] The invention relates to the technical field of coil coatings, in particular to a bottom and top coat for deep embossing resistant household appliance panels and a preparation method thereof. Background Art

[0002] With the increasing use of color-coated steel in the home appliance industry, competition is becoming increasingly fierce. To reduce costs and improve cost-effectiveness, some domestic color-coated steel mills are reducing steel plate thickness and utilizing embossing to increase both thickness and strength, achieving cost savings without sacrificing quality. This process, widely used in the production of refrigerator side panels, places increasing demands on the paint coating. The paint film must possess high flexibility and shear strength, while also maintaining integrity and ductility under mechanical tensile deformation. Consequently, the film must possess a certain strength and strong adhesion.

[0003] Conventional pre-coated coil coatings for appliance panels are mostly multi-coat systems. The front of the appliance panels is generally constructed using a "two-coat, two-bake" construction process, where a primer is applied to the front of the substrate followed by a topcoat. This traditional "two-coat, two-bake" process is not only cumbersome to construct and has high production costs, but also wastes energy and is time-consuming and labor-intensive. However, a primer-and-topcoat for deep-embossed appliance panels that combines primer and topcoat into one, while also offering excellent corrosion resistance and decorative properties, can effectively address these issues. Construction requires only a "one-coat, one-bake" process, and the resulting paint film not only possesses the sealing and corrosion resistance of the primer, but also the decorative and exterior protection of the topcoat. This effectively reduces the construction process flow, lowers costs, significantly shortens the production cycle, and improves actual production efficiency. However, the color-coated panel industry currently lacks a mature primer-and-topcoat product that can meet the aforementioned performance requirements after deep embossing. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a bottom and top coat for deep embossing resistant home appliance panels and a preparation method thereof. The bottom and top coat can greatly improve the deep embossing resistance of the color-coated panels, so that the embossed color-coated panels have strong flexibility, surface strength and ductility, and higher adhesion.

[0005] In a first aspect, the present invention provides a bottom and top coating for deep embossing resistant household appliance panels, which is achieved by adopting the following technical solutions.

[0006] A bottom and top coat for deep embossing-resistant household appliance panels, comprising the following components in parts by weight:

[0007] 20-35 parts of modified polyester resin;

[0008] 3-10 parts of high molecular weight polyester resin;

[0009] 6-10 parts of curing agent;

[0010] 20-35 parts of pigments and fillers;

[0011] 0.4-1 part wax powder;

[0012] 2-3 parts of additives;

[0013] 15-30 parts of solvent;

[0014] Wherein, the modified polyester resin is a polyester polyurethane resin, which is prepared by reacting a polyester polyol resin with a diisocyanate compound.

[0015] Furthermore, the preparation method of the modified polyester resin comprises the following steps:

[0016] a. Under the action of a catalyst, the diol and the dibasic acid are subjected to an esterification reaction to obtain a linear hydroxyl-terminated polyester resin prepolymer;

[0017] b. In the presence of a catalyst, the linear hydroxyl-terminated polyester resin prepolymer and the diisocyanate compound prepared in step a are subjected to an addition polymerization reaction to obtain a hydroxyl-terminated polyester polyurethane resin.

[0018] Furthermore, in the esterification reaction of step a, the ratio of the molar number of hydroxyl groups in the diol to the molar number of carboxyl groups in the dibasic acid is 1.2-1.5:1.

[0019] Furthermore, the dibasic acid is selected from a mixture of one or more of adipic acid, isophthalic acid, hexahydrophthalic anhydride, 1,4-cyclohexanedicarboxylic acid, and 1,2-cyclohexanedicarboxylic acid.

[0020] Furthermore, the diol is selected from one or more mixtures of neopentyl glycol, methylpropylene glycol, 1,4-cyclohexanedimethanol, 1,2-cyclohexanedimethanol, and 3-methyl-1,5-pentanediol.

[0021] Furthermore, the esterification reaction conditions of step a are: heating to 140-145°C at a rate of 10-15°C / h for reflux reaction, keeping warm at 200-205°C for 1-2 hours, and then heating to 230-235°C over 2-3 hours for keeping warm until the acid value is stable.

[0022] Furthermore, the esterification reaction catalyst in step a is monobutyltin oxide, and the added amount of the catalyst is 0.03-0.3% of the total mass of the reaction materials in step a.

[0023] Furthermore, in the addition polymerization reaction of step b, the ratio of the molar number of hydroxyl groups in the linear hydroxyl-terminated polyester resin prepolymer to the molar number of isocyanate groups in the diisocyanate compound is 1:0.7-0.9.

[0024] Furthermore, the diisocyanate compound is selected from one or a combination of aromatic diisocyanate and alicyclic diisocyanate.

[0025] Specifically, the diisocyanate compound is selected from one or more of toluene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, and dicyclohexylmethane diisocyanate.

[0026] The addition polymerization reaction conditions of step b are: heating to 50-60°C over 1-2 hours, reacting for 1-2 hours, then heating to 65-70°C, reacting for 2-3 hours, and continuing to heat to 70-80°C and keep reacting until the measured system NCO is ≤5mgNCO / g.

[0027] Furthermore, the addition polymerization catalyst in step b is dibutyltin dilaurate, and the added amount of the catalyst is 0.1 to 0.2% of the mass of the total reaction materials in step b.

[0028] Furthermore, the high molecular weight polyester resin is a linear saturated polyester resin with terminal hydroxyl functional groups, with an acid value of 0-8 mgKOH / g, a number average molecular weight of 10,000-20,000, and a hydroxyl value of 2-10 mgKOH / g.

[0029] Specifically, the high molecular weight polyester resin can be selected from at least one of the following commercially available models: CH550, CH470, CH541, CH460 (Hanhai New Materials Company); ES160, ES410, ES420, ES450 (SK Company of South Korea).

[0030] Furthermore, the curing agent is a combination of a blocked polyisocyanate resin and an amino resin, and the mass ratio of the blocked polyisocyanate resin to the curing agent is 5:95-20:80.

[0031] Specifically, the amino resin is a fully methylated amino resin, such as the commercially available resin products with model number CYMEL303 from Cytec and model number Resimene-747 from Solutia. The blocked polyisocyanate resin is a trimer isocyanate, which can be selected from DESMODUR BL3175 provided by Bayer, B1358 provided by Evonik, or similar commercially available blocked isocyanate resins.

[0032] Furthermore, the pigment and filler is selected from one or a combination of titanium dioxide, carbon black, red iron oxide, and yellow iron oxide.

[0033] Furthermore, the pigment filler also includes an environmentally friendly anti-rust pigment of polyphosphate SRPP and calcium ion exchange pigment MS780, the added amount of the environmentally friendly anti-rust pigment is 4.5-5.5wt% of the total paint amount, and the mass ratio of polyphosphate SRPP to calcium ion exchange pigment MS780 is 1:5-1:3.

[0034] Furthermore, the wax powder is selected from at least one of polytetrafluoroethylene wax, fluorine-modified polyethylene wax, and fluorine-modified synthetic wax.

[0035] Specifically, the wax powder is selected from at least one of Fluo HT, Synfluo 178XF, and Synfluo 180XF produced by American Micronized Powder Company.

[0036] Furthermore, the auxiliary agent is selected from at least one of a dispersant, a defoaming agent, a leveling agent, an adhesion promoter, and a curing catalyst.

[0037] Furthermore, the dispersant is selected from at least one of AFCONA-4010, AFCONA-4017, AFCONA-4060, AFCONA-4070 and AFCONA-4080 produced by AFCONA.

[0038] Furthermore, the defoaming agent is a non-silicon defoaming agent, selected from at least one of BYK company models BYK-054, BYK352, BYK-057, and BYK-1795.

[0039] Furthermore, the leveling agent is a non-silicone leveling agent, selected from at least one of AFCONA-3700, AFCONA-3750, AFCONA-3773, AFCONA-3775, AFCONA-3777, and AFCONA-3779 produced by AFCONA.

[0040] Furthermore, the adhesion promoter is a phosphate modified polymer, selected from at least one of Lubrizol 2063, Tech-7205, and ADP.

[0041] Furthermore, the curing catalyst includes an acid catalyst, which is selected from at least one of the models NACURE 1051, NACURE 2500, and NACURE 5225 of King's Company, USA.

[0042] Furthermore, the solvent is selected from at least one of butanol, propylene glycol methyl ether acetate, cyclohexanone, S-100# aromatic solvent, S-150# aromatic solvent, and dibasic acid ester DBE.

[0043] In a second aspect, the present invention provides a method for preparing a bottom and top coat for deep embossing resistant household appliance panels, which is achieved by adopting the following technical solutions.

[0044] A method for preparing the above-mentioned bottom and top coat for deep embossing-resistant household appliance panels comprises the following steps:

[0045] S1. The modified polyester resin 30-50% of the total mass of the modified polyester resin, the dispersant additives, pigments, fillers, wax powder mixed, and then add 30-50% of the total mass of the solvent solvent, grinding to obtain a slurry, which is sanded to 15μm or less;

[0046] S2. Add the remaining modified polyester resin, high molecular weight polyester resin, and the remaining additives except the dispersant to the slurry and mix; then add the curing agent and the remaining solvent, mix, and filter to obtain a bottom and top coat for deep embossing-resistant home appliance panels.

[0047] This application has the following beneficial effects.

[0048] 1. The present invention synthesizes a polyester polyurethane resin by modifying the polyester resin polymer chain, namely, by conducting an addition polymerization reaction between a linear hydroxyl-terminated polyester resin prepolymer and a diisocyanate compound. The modified polyester resin contains a certain amount of urethane bonds, which not only gives the coating excellent flexibility and adhesion, but also surpasses ester bonds in hydrolytic stability, salt spray resistance, and acid resistance.

[0049] 2. The present invention conducts an addition polymerization reaction between a linear hydroxyl-terminated polyester resin prepolymer and a diisocyanate compound to obtain a polyester polyurethane resin. By varying the types of diol, dibasic acid, and diisocyanate compounds, resins with different molecular structures and properties can be obtained, achieving molecular structure adjustability, and ultimately obtaining deep embossing-resistant home appliance panels with different functionalities.

[0050] 3. The present invention provides a primer-and-topcoat for deep-embossing-resistant appliance panels, combining primer and topcoat into one. Application requires only a "one-coat, one-bake" process, significantly shortening the production cycle and improving actual production efficiency. Compared to the traditional "two-coat, two-bake" process, curing energy consumption is reduced by 40%-50%, resulting in significant energy savings and consumption reductions.

[0051] 4. The primer and topcoat prepared by the present invention can be widely used in coil coatings for household appliance panels resistant to deep embossing, especially side panels of household appliance refrigerators. It overcomes the shortcomings of topcoats in the prior art in terms of deep embossing resistance, gives the coating excellent embossing resistance to MEK, and also improves the adhesion and machinability of the coating.

[0052] 5. The preparation method of the polyester topcoat of the present invention is simple, meets the production requirements of green and environmental protection, and is easy to produce on a large scale. DETAILED DESCRIPTION

[0053] The present patent application is further described below with reference to the embodiments.

[0054] Unless otherwise specified, the experimental methods used in the following preparation examples and examples are conventional methods; the materials, reagents, etc. used in the following preparation examples and examples are all commercially available unless otherwise specified.

[0055] Preparation Example

[0056] Preparation of modified polyester resin

[0057] The preparation methods of modified polyester resins A to Q in Table 1 are as follows (modified polyester resins P and Q are both adjusted based on modified polyester resin M):

[0058] (1) Add diol (I in Table 1), dibasic acid (II in Table 1), 0.25 g of monobutyltin oxide, and 80 g of xylene to a clean reaction bottle equipped with a stirrer, a thermometer, a water separator, a condenser, and an inert gas inlet. Under continuous stirring and in an inert atmosphere, after the components are fully mixed, heat the material to 140° C. at a rate of 10° C. / h and reflux for reaction for 1 hour, then heat the material to 200° C. and keep the temperature for reaction for 2 hours, then heat the material to 230° C. and keep the temperature for reaction until the acid value of the reaction system is stable, and cool the material to obtain a linear polyester resin with terminal hydroxyl groups;

[0059] (2) Add a diisocyanate compound (see III in Table 1 for details) and 0.5 g of dibutyltin dilaurate, then slowly heat the mixture to 60°C for reaction for 1 hour, then heat the mixture to 70°C for reaction for 1 hour, and continue heating the mixture to 80°C for reaction until the NCO% of the system is ≈ 0 (the reaction endpoint is determined by hexachloropyridine-chlorobenzene titration method with bromocresol green as the indicator). Cool the mixture while stirring thoroughly, and filter the mixture. The resulting filtrate is the modified polyester resin.

[0060] The specific selection of each reactant is shown in Table 1:

[0061] Table 1

[0062]

[0063]

[0064]

[0065]

[0066] Example

[0067] Based on the modified polyester resins in Table 1, primer and topcoat for deep embossing resistant home appliance panels were prepared respectively. The specific amount of each raw material is shown in Table 2. The preparation process is as follows:

[0068] Step (1): 30-50% of modified polyester resin, dispersant, pigment, filler, and wax powder are mixed, and then 30-50% of solvent is added, and the mixture is ground to obtain a slurry, wherein the mixture is sand-ground to a particle size of less than 15 μm;

[0069] Step (2): adding the remaining modified polyester resin, high molecular weight polyester resin, and the remaining additives except the dispersant to the slurry obtained in step (1) and mixing; then adding the curing agent and the remaining solvent, mixing and filtering to obtain the bottom and top coating for deep embossing resistant home appliance panels.

[0070] Table 2 Material input conditions in step (1) and step (2) of Example 1-40

[0071]

[0072]

[0073]

[0074]

[0075]

[0076]

[0077]

[0078]

[0079]

[0080]

[0081] It should be noted that: Comparative Example 1 is based on Example 9, except that the modified polyester resin is adjusted, while the other components remain unchanged. Specifically, during the synthesis of the modified polyester resin, aromatic diisocyanate and alicyclic diisocyanate are not contained, and aliphatic isocyanate is used; Comparative Example 2 is based on Example 9, except that the modified polyester resin is adjusted, while the other components remain unchanged. Specifically, during the synthesis of the modified polyester resin, no isocyanate is contained; Comparative Example 3 is based on Example 27, except that the curing agent is adjusted, while the other components remain unchanged. Specifically, the curing agent is only amino resin; Comparative Example 4 is based on Example 27, except that the curing agent is adjusted, while the other components remain unchanged. Specifically, the curing agent is only a blocked polyisocyanate resin; Comparative Example 5 adjusts the anti-rust filler on the basis of Example 28, and the other components remain unchanged. Specifically, the anti-rust filler contains only polyphosphate SRPP; Comparative Example 6 adjusts the anti-rust filler on the basis of Example 28, and the other components remain unchanged. Specifically, the anti-rust filler contains only calcium ion exchange pigment MS780; Comparative Example 7 adjusts the high molecular weight polyester resin on the basis of Example 28, and the other components remain unchanged. Specifically, the resin C1223 used in the high molecular weight polyester resin is a linear saturated polyester resin (number average molecular weight less than 10,000) produced by Hanhai New Materials.

[0082] Performance testing

[0083] Coating board making process:

[0084] Coating plate making: The obtained deep embossing resistant home appliance plate is coated with a bottom and top coat on the pretreated galvanized steel plate using a wire rod roller, baked in a 300℃ oven for 40s, the metal plate temperature PMT: 224℃, to obtain a bottom and top coat film with a film thickness of 12-15μm.

[0085] Embossed plate sample preparation: Place the prepared sample into the embossing machine to obtain a sample with an embossing depth of 70-80μm.

[0086] After testing, the bottom-and-top coatings formed by the above-mentioned operations of the bottom-and-top coatings for deep embossing-resistant household appliance panels of Examples 1-30 all meet various quality standards. The various quality standards and results are specifically shown in Table 3:

[0087] Table 3

[0088]

[0089]

[0090] Note: The rubbing resistance test is a relative displacement test, which simulates the relative displacement force caused by the topcoat and the backcoat being in close contact during the transportation of the color-coated coil. The method is to select an ordinary topcoat plate and the backcoat plate to be in close contact, at 50°C and 10kg force, and rub the topcoat plate and the backcoat plate (evaluation criteria: no paint falling off, slight paint falling off, some paint falling off, severe paint falling off).

[0091] Other properties not listed in this application form are known to those skilled in the art and can meet the performance requirements.

[0092] After testing, the bottom-and-top coatings formed by the above-mentioned operations for the bottom-and-top coatings for deep embossing-resistant household appliance panels of Comparative Examples 1-7 have performance test results as shown in Table 4 below:

[0093] Table 4

[0094]

[0095]

[0096] From the experimental results in Table 3 and Table 4, we can see that:

[0097] (1) The primer and topcoat for home appliance panels prepared by the present invention are suitable for the surface of hot-dip galvanized steel sheets, electro-galvanized steel sheets, cold-rolled steel sheets, zinc-aluminum-magnesium steel sheets, and aluminum-zinc-coated steel sheets. The coil primer and topcoat are combined into one, and only a "one-coat-one-bake" process is required during roller coating, which greatly shortens the production cycle and improves actual production efficiency. Compared with the traditional "two-coat-two-bake" process, the energy consumed for curing is reduced by 40%-50%, which significantly saves energy and reduces consumption. It can be widely used in coil coatings for home appliance panels that are resistant to deep embossing, especially the side panels of home appliance refrigerators. It overcomes the shortcomings of the topcoat in the prior art in terms of deep embossing resistance, gives the coating excellent embossing resistance to MEK, and also improves the adhesion and machinability of the coating. It is in line with the development trend of the color-coated plate industry and has broad market and application prospects.

[0098] (2) The modified polyester resin in Comparative Example 1 does not contain aromatic diisocyanate and alicyclic diisocyanate, but uses aliphatic isocyanate. It does not contain aromatic (phenyl ring) or alicyclic (aliphatic) isocyanate with a rigid hard structure, and its adhesion to the metal substrate is insufficient, resulting in poor mechanical properties of the embossed plate.

[0099] (3) The modified polyester resin in Comparative Example 2 does not contain isocyanate, so the molecular weight of the modified polyester resin finally synthesized becomes smaller, the hydroxyl value becomes larger, and it does not contain urethane bonds. The coating resistance is poor and the adhesion is weak.

[0100] (4) In Comparative Example 3, the curing agent only contains amino resin. Compared with Example 27, the coating is harder, has poorer flexibility, and has weaker adhesion.

[0101] (5) In Comparative Example 4, the curing agent only contains a blocked polyisocyanate resin, the paint film is relatively soft, the degree of crosslinking is insufficient, and the hardness is insufficient, but the resistance is better.

[0102] (6) In Comparative Example 5, the rust-proof filler contains only polyphosphate SRPP; in Comparative Example 6, the rust-proof filler contains only calcium ion exchange pigment MS780. The calcium ion exchange silica gel can intercept corrosive ions entering the coating on the silica surface, exchange them with calcium ions adsorbed on the silica gel surface, and transfer the released calcium ions to the metal coating interface to form a dense and impermeable calcium ion layer, which plays a role in blocking corrosive ions and thus protecting the substrate. When water vapor penetrates into the coating, the phosphate rust-proof pigment will dissociate into tripolyphosphate ions with strong complexing ability, which react with iron ions to form a complex protective film with iron tripolyphosphate as the main component. This phosphate protective film is insoluble in water, has high hardness, and has strong adhesion to the substrate metal. It can effectively prevent the further progress of the corrosion reaction and achieve an excellent anti-corrosion effect. However, pure calcium ion exchange pigments or polyphosphates cannot maximize the salt spray resistance performance. Two different types of rust-proof fillers need to be used in combination to produce a synergistic effect.

[0103] (7) In Comparative Example 7, the base resin does not contain a high molecular weight polyester resin. The higher the relative molecular mass of the polyester resin in the coil coating system, the stronger the adhesion of the coating to the metal substrate. Therefore, the adhesion of the coating in this comparative example deteriorates.

[0104] The embodiments of this specific implementation method are all preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the scope of protection of the present invention.

Claims

1. A bottom and top coat for deep embossing resistant home appliance panels, characterized by: The composition comprises the following components in parts by weight: 20-35 parts of modified polyester resin; 3-10 parts of high molecular weight polyester resin; 6-10 parts of curing agent; 20-35 parts of pigments and fillers; 0.4-1 part wax powder; 2-3 parts of additives; 15-30 parts of solvent; The modified polyester resin is a polyester polyurethane resin, which is prepared by reacting a polyester polyol resin with a diisocyanate compound. The preparation method of the modified polyester resin comprises the following steps: a. Under the action of a catalyst, the diol and the dibasic acid are subjected to an esterification reaction to obtain a linear hydroxyl-terminated polyester resin prepolymer; b. In the presence of a catalyst, the linear hydroxyl-terminated polyester resin prepolymer prepared in step a and a diisocyanate compound are subjected to addition polymerization to obtain a hydroxyl-terminated polyester polyurethane resin; In the esterification reaction of step a, the ratio of the molar number of hydroxyl groups in the diol to the molar number of carboxyl groups in the dibasic acid is 1.2 to 1.5:1; in the addition polymerization reaction of step b, the ratio of the molar number of hydroxyl groups in the linear hydroxyl-terminated polyester resin prepolymer to the molar number of isocyanate groups in the diisocyanate compound is 1:0.7 to 0.9; the diisocyanate compound is selected from one or a combination of aromatic diisocyanates and alicyclic diisocyanates; The high molecular weight polyester resin is a linear saturated polyester resin with terminal hydroxyl functional groups, with an acid value of 0-8 mgKOH / g, a number average molecular weight of 10,000-20,000, and a hydroxyl value of 2-10 mgKOH / g; The curing agent is a combination of a blocked polyisocyanate resin and an amino resin, and the mass ratio of the blocked polyisocyanate resin to the curing agent is 5:95-20:80; The pigments and fillers are selected from one or a combination of titanium dioxide, carbon black, red iron oxide, and yellow iron oxide; the pigments and fillers also include environmentally friendly anti-rust pigments of polyphosphate SRPP and calcium ion exchange pigment MS780, the added amount of the environmentally friendly anti-rust pigment is 4.5-5.5wt% of the total paint amount, and the mass ratio of polyphosphate SRPP to calcium ion exchange pigment MS780 is 1:5-1:

3.

2. The bottom and top coat for deep embossing resistant household appliance panels according to claim 1, characterized in that: The esterification reaction conditions of step a are: heating to 140-145°C at a rate of 10-15°C / h for reflux reaction, keeping warm at 200-205°C for 1-2h, then heating to 230-235°C over 2-3h for reaction until the acid value is stable; the addition polymerization reaction conditions of step b are: heating to 50-60°C over 1-2h for reaction for 1-2h, then heating to 65-70°C for reaction for 2-3h, and then heating to 70-80°C for reaction until the NCO content of the system is ≤5mgNCO / g.

3. A method for preparing the bottom and top coat for deep embossing resistant household appliance panels according to claim 1 or 2, characterized in that: The following steps are involved: S1. The modified polyester resin 30-50% of the total mass of the modified polyester resin, the dispersant additives, pigments, fillers, wax powder mixed, and then add 30-50% of the total mass of the solvent solvent, grinding to obtain a slurry, which is sanded to 15μm or less; S2. Add the remaining modified polyester resin, high molecular weight polyester resin, and the remaining additives except the dispersant to the slurry and mix; then add the curing agent and the remaining solvent, mix, and filter to obtain a bottom and top coat for deep embossing-resistant home appliance panels.

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